Hyper extremely red objects in the Subaru Deep Field: Evidence for primordial elliptical galaxies in the dusty starburst phase

We report the observational analyses and theoretical interpretations of unusually red galaxies in the Subaru Deep Field (SDF). A careful analysis of the SDF data revealed a population with unusually red near-infrared (NIR) colors of J-K greater than or similar to 3-4, with a higher confidence than the previous SDF result. Their surface number density drastically increases at K greater than or similar to 22 and becomes roughly the same as that of dusty starburst galaxies detected by submillimeter observations in recent years. These colors are even redder than the known population of the extremely red objects (EROs) and are too red to be explained as passively evolving elliptical galaxies, which are the largest population of EROs. Hence, these hyper extremely red objects should be considered as a distinct population from EROs. We discuss several possible interpretations of these enigmatic objects, and we show that these red NIR colors, the K-band and submillimeter flux, and the surface number density are quantitatively best explained by primordial elliptical galaxies reddened by dust and still in the starburst phase of their formation at z similar to 3.